Photo-electric relay



March 30, 1965 F. P. DUNlGAN 3,176,196

PHOTO-ELECTRIC RELAY Filed Aug. 9, 1961 FIG. 1

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United States Patent 3,176,196 PHOTO-ELECTRIC RELAY Francis P. Dunigan, Holden, Mass, assignor to Machinery Electrification, Inc., Northhoro, Mass, a corporation of Massachusetts Filed Aug. 9, 1961, Ser. No. 130,329 4 Claims. (Cl. 317-125) This invention relates to a photoelectric relay and more particularly to apparatus arranged to connect or disconnect an electrical circuit in response to the intensity of light.

A cadmium selenide photo resistor is capable of offering very large changes of resistance with small changes of light intensity. These resistors have been used to operate a small relay directly in series with the cell, thus eliminating the need for a vacuum tube and amplifier as has been necessary in the past with photo-electric cells. Generally speaking, such a simple relay is operated on direct current obtained from a rectifier and a capacitor as part of the assembly. However, it is possible to eliminate the rectifier and capacitor and to operate the device on 110 volts, 60 cycle power. The circuit, then, becomes a simple series circuit of the relay coil and the photo resistor. However, a problem is presented by the fact that the relay does not operate in a clean manner; instead, it buzzes in and out as light is alternately applied and removed. In addition to the noise, the buzz has an other disadvantage; the fact that the relay is buzzing indicates that the contact pressure is varying in accordance with the 60 cycle current and this can cause arcing or excessive sparking of the contacts. This, of course, results in failure of the contact in a very short time. These and other difiiculties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a photo-electric relay which may be operated from alternating current electricity without rapid deterioration of the relay contacts.

Another object of this invention is the provision of a photo-electric relay to be operated from alternating current electricity which makes and breaks contact without excessive noise.

A further object of the present invention is the provision of a relay making use of a cadmium selenide photo resistor which may be operated by alternating current electricity Without noise or deterioration of the relay contacts.

It is another object of the instant invention to provide a relay operated by light falling on a photo resistor which open-ates on alternating current electricity to give quick and clean making or breaking of contact.

With these and other objects in view, as will be apparent to those skilled in the art, invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

The character of the invention, however, may be best understood by reference to one of its structural forms, as illustrated by the accompanying drawings in which:

FIG. 1 is a perspective view of a relay embodying the principles of the present invention;

FIG. 2 is a vertical sectional view of the relay taken on the line II-II of FIG. 1;

FIG. 3 is an enlarged vertical sectional view of a portion of the invention taken on the line IIIIII of FIG. 2; and

FIG. 4 is an electrical schematic view of the invention.

Referring first to FIG. 1, wherein are best shown the general features of the invention, the relay, indicated generally by the reference numeral 10, is shown as consisting of a housing 11 in which is mounted a cadmium selenide photo resistor 12, a lens 13, and a relay element 14. The housing is formed of plastic material and was provided with a front wall 15, a rear Wall 16 joined by a bottom 17. A groove 18 extends around the edges of the housing and is adapted to receive the edges of a U-shaped lighttight closure (not shown) but which serves to enclose all of the apparatus with the exception of the lens 13. Fastened to the rear wall 16 by means of bolts 19 is an L-shaped support 21 having a vertical portion 22 parallel to and slightly spaced from the rear wall 16 of the housing and a horizontal portion 23 which is parallel to and spaced from the bottom 17 of the housing. The vertical portion 22 is formed with a circular aperture 24 in which the cadmium selenide photo resistor 12 is mounted, there being a rubber pad 25 cemented to the surface of the wall 16 and to the resistor 12, so that the resistor floats and yet is restrained by the edges of the aperture 24. The front wall 15 of the housing is formed with a tubular hood 26 in which is molded an aluminum threaded sleeve 27. This sleeve is threadedly engaged with a ring 28 in which the lens 13 is mounted.

The cadmium selenide photo resistor 12 is of the wellknown type which has a low resistance when light falls on it and a high resistance when light does not fall on it. Mounted on the horizontal portion 23 of the support 21 is a sheet metal bracket 29, best shown in FIG. 3. The bracket is provided with a base portion 31 which is fastened to the upper surface of the horizontal portion 23 of the support 21. On this base portion is mounted a relay coil 32 having an iron core 33. The bracket 29 is provided with a vertical portion 34 having in the lower portion a lug 35 and in the upper portion an aperture 36. Through the aperture extends a movable element 37 of the relay. A portion of the movable element extends through the aperture 36 and overlies the lug 35; a coil spring 38 extends in tension between the two to bias the movable element 37 in an upward direction. The outer end of the movable element is provided with a vertical insulated plate 39 formed of a non-electrically conducting material. At the top of the vertical portion 34 the bracket 29 is provided with a short table portion 41 having mounted on its upper surface an insulating plate 42, a contact finger 43 having an apertured electrical attachment, lugs extending rearwardly therefrom, another insulating plate 44, a contact finger 45 having an electrical attachment lug extending rearwardly therefrom, an insulating plate 46, a contact finger 47 with a rearwardlyextending lug, and lastly another insulating plate 48. The central contacting finger 45 extends at its forward end through the plate 39 and moves upwardly and downwardly with the plate and with the movable element 37 of the relay element. The plates and fingers are fastened to the table portion 41 by means of screws in the usual way. In its normal position with the coil 32 unenergized the spring 38 biases the movable element 37 upwardly; this causes the plate 39 to carry the central contact finger 45 into electrical contact with the upper contact finger 47; when the coil 32 is energized, however, the movable element 37 moves downwardly into contact with the core 33. This movement carries the plate 39 and the central contact finger 45 so that the last-named finger contacts the lower contact finger 43.

Mounted on the movable element 37 between the lens 13 and the reeds or contact fingers 43, 45 and 47 is a shield 49 formed of a generally opaque material. The shield has a height such that, when the coil 32 is unenergized and the movable element 37 is in its upper position, it cuts approximately in two the rays of light extending between the lens 13 and the photo resistor 12. The section of the ray of light in the area of the shield is shown by the dotted line circle 51 in FIG. 3 and when the coil 32 is energized and the movable element 37 is in its downward position against the core 33, however, the shield 49 has moved entirely out of the circle.

Referring particularly to FIG. 4, which shows the electrical connections, a line 52 is connected to one side of a source of alternating current electricity (not shown). The other end of the line 52 is connected to one side of the photo resistor 12. The other side of the photo resistor is connected by a line 53 to one side of the coil 32 of the relay element 14. The other side of this coil is connected by a line 54 to the other side of the alternating current source. As is usual in most relays, there are binding posts to which a circuit may be connected for use as a normally closed circuit and others which may be used as a normally-open circuit. The finger 45 and the finger 47 serve as a normally-closed portion of the relay while the finger 45 and the finger 43 serve as a normally-open portion. These fingers may be inserted in an electrical circuit to perform switching operations as desired.

The operation of the invention will now be readily understood in view of the above description. With the apparatus connected to the alternating current circuit, with the closure over the housing 11, and with no light coming through the lens 13, the photo resistor 12 has a very high resistance. For that reason, no current fiows through the coil 32 and the movable element 37 is in its upper position, thus closing the circuit between the finger 45 and the finger 47 and keeping open the circuit between the finger 45 and the finger 43. When light is admitted to the lens 13, however, it falls on the photo resistor 12 and causes its resistance to drop very rapidly. When this happens, current passes through the line 54, the coil 32, the line 53, the photo resistor 12, and the line 52. The energization of the coil 32 in this way causes an electromagnetic field to be set up around the iron core 33 and draws the movable element 37 downwardly into contact with the core. The movement of the member 37 causes a similar downward movement of the plate 39 which carries the finger 45 with it and into contact with the finger 43, thus closing that circuit and opening the circuit between the finger 45 and the finger 47. The current which passes through the relay coil 32, however, is alternating current and for that reason the electromagnetic field set up around the core 33 is built up and falls off 60 times per second; this normally would cause a vibratory movement of the movable element 37 downwardly and cause a buzzing noise in the contact fingers. Actually, if the movable element 37 moves up and down or vibrates slightly as it moves in its downward direction, clean breaking and making of the electrical contact is prevented. The result would be not only a noisy operation and an operation which would be poor from an electrical switching point of view, but also result in rapid deterioration of the silver contact discs on the fingers. This is the type of undesirable operation that would take place were it not for the shield 49. However, in the present case, when the light passes through the lens 13, approximately onehalf the light is cut off by the shield 49. When the movable element 37 starts downwardly, it carries the shield with it and the slightest movement of the shield downwardly exposes a very much larger part of thelight in the circle 51 of the light ray which is falling on the photo resistor 12, so that the movement downwardly is greatly accelerated the moment it has started. The greater exposure of light to the photo resistor causes even greater energization of the coil 32 and the movable member 37 4 moves downwardly into position rapidly without giving the alternating current an opportunity to draw it up and down or to vibrate it during its movement.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired, to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent is:

1. A photo-electric relay for use with a source of alternating current electricity, comprising a photo resistor, a relay coil, the resistor and the coil being connected in series for connection across the source, means causing the light to pass in a defined path to the resistor, amovable element associated with the coil and adapted on movement to bring about a switching function, a shield actuated by the movable element from a first position in the said path when the coil is non-energized to a second position at least partly removed from the said path when the coil is energized.

2. A photo-electric relay for use with a source of alternating current electricity, comprising a photo resistor which has a high resistance when light falls on it and a low resistance when no light falls on it, a relay coil, the resistor and the coil being connected in series for connection across the source, means causing light to pass in a defined path to the resistor, a movable element associated with the coil and adapted on movement to bring about a switching function, a shield actuated by the movable element from a first position in the said path when the coil is unenergized to a second position at least partly removed from the said path when the coil is energized.

3. A photo-electric relay for use with a source of alternating current electricity, comprising a photo resistor, a relay coil, the resistor and the coil being connected in series for connection across the source, a lens causing light to pass in a defined ray to the resistor, a movable element associated with the coil and adapted on move ment to bring about a switching function, a shield actuated by the movable element from a first position interxrupting a substantial area of the said ray when the coil is unenergized to a second position when the coil is energizcd, the shield interruptingconsiderably less area of the said ray when in the second position than when in the first position.

4. A relay adapted to be energized by a source of alternating current electricity, comprising a cadmium selenide photo resistor which has a high resistance when light falls on it and a low resistance when no light falls on it, a relay coil, the resistor and the coil being joined in series for connection across the source, a lens causing light to pass in a defined ray to the resistor,-a movable element associated with the coil and adapted on movement to bring about a switching function, an opaque shield mounted on the movable element and movable with it from a first position interrupting a substantial area of the said ray when the coil is unenergized to a second position when the coil is energized, the shield interrupting considerably less area of the said ray when in the second position than when in the first position.

. References Cited in the file of this patent UNITED STATES PATENTS 1,788,111 Knowles Jan. 6, 1931 2,913,637 Bayley Nov. 17, 1959 

1. A PHOTO-ELECTRIC RELAY FOR USE WITH A SOURCE OF ALTERNATING CURRENT ELECTRICITY, COMPRISING A PHOTO RESISTOR, A RELAY COIL, THE RESISTOR AND THE COIL BEING CONNECTED IN SERIES FOR CONNECTION ACROSS THE SOURCE, MEANS CAUSING THE LIGHT TO PASS IN A DEFINED PATH TO THE RESISITOR, A MOVABLE ELEMENT ASSOCIATED WITH THE COIL AND ADAPTED ON MOVEMENT TO BRING ABOUT A SWITCHING FUNCTION, A SHIELD ACTUATED BY THE MOVABLE ELEMENT FROM A FIRST POSITION IN THE 